Its common knowledge. Even if you somehow get away with not cutting your PR card during the oath ceremony, using it to enter Canada will set off alarms as the card would be deactivated. Its like driving on a suspended/revoked driver's license, except in this case, getting caught is guaranteed when you swipe that card at the Kiosk when you're trying to enter Canada.
You are no longer a Permanent resident from the time you've taken oath and signed the oath form. You CANNOT use a PR card beyond that point. You'll be asked to cut it into several pieces (2 or 4 pieces, depending on the office) at the end of the citizenship ceremony.
If you still want proof for this common knowledge, read the PDF that is attached to your oath invitation email.
Also, read this =>
https://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=067&top=10